Bug 513365

Summary: KDE 6.4.5 on AMD 4800U: 50% brightness triggers blackscreen via XF86MonBrightnessDown
Product: [Plasma] kwin Reporter: EC Optino <alanqa-ops>
Component: inputAssignee: KWin default assignee <kwin-bugs-null>
Status: NEEDSINFO WAITINGFORINFO    
Severity: normal CC: duha.bugs, xaver.hugl
Priority: NOR    
Version First Reported In: 6.4.5   
Target Milestone: ---   
Platform: Kubuntu   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description EC Optino 2025-12-14 15:27:42 UTC 
SUMMARY
Lenovo Xiaoxin Air15 (AMD 4800U) KDE 6.4.5: 50% brightness + XF86MonBrightnessDown triggers temp blackscreen (X11/Wayland)

STEPS TO REPRODUCE
1. Adjust the laptop’s built-in display brightness to exactly 50%
2. Press the XF86MonBrightnessDown hardware shortcut (backlight decrease key)
3. (Optional) Press XF86MonBrightnessUp to test display recovery

OBSERVED RESULT
The display immediately goes black temporarily when Step 2 is executed. The screen only recovers after pressing XF86MonBrightnessUp (backlight increase key).  
This issue occurs regardless of whether the brightness shortcut is mapped in KDE’s global shortcut settings, and is reproducible in both X11 and Wayland Plasma sessions. Stopping the PowerDevil service does not resolve the bug.

EXPECTED RESULT
The display brightness should decrease normally from 50% to a lower level without any blackscreen or display interruption, with no need for manual recovery via the brightness-up key.

SOFTWARE/OS VERSIONS
Operating System: Kubuntu 25.10
KDE Plasma Version: 6.4.5
KDE Frameworks Version: 6.17.0
Qt Version: 6.9.2
Kernel Version: 6.17.0-8-generic (64-bit)
Graphics Platform: Wayland
Processors: 16 × AMD Ryzen 7 4800U with Radeon Graphics
Memory: 16 GiB of RAM (15.0 GiB usable)
Graphics Processor: AMD Radeon Graphics
Manufacturer: LENOVO
Product Name: 82GL
System Version: Lenovo XiaoXinAir 15ARE 2021

ADDITIONAL INFORMATION
Hardware: Lenovo Xiaoxin Air15 2021 (Ryzen Edition), AMD Ryzen7 4800U (integrated Radeon Graphics), single built-in laptop display  
Platform:  The bug does not occur in GNOME desktop (kubuntu 25.10) or Windows 11 on the same hardware
Comment 1 Zamundaaa 2025-12-15 12:25:20 UTC 
Does running
> kscreen-doctor output.1.brightness.40
do the same?
Comment 2 EC Optino 2025-12-16 04:20:15 UTC 
(In reply to Zamundaaa from comment #1)
> Does running
> > kscreen-doctor output.1.brightness.40
> do the same?

> kscreen-doctor output.1.brightness.40
(,45,50) does not trigger blackscreen and adjusts screen brightness as expected
Comment 3 EC Optino 2025-12-16 04:36:45 UTC 
New additional:
Information from brightnessctl (https://github.com/Hummer12007/brightnessctl):
Device 'amdgpu_bl1' of class 'backlight':
        Current brightness: 32768 (50%)
        Max brightness: 65535
Test:
Only current brightness = 32768 (50%) then press BrightnessDown triggers blackscreen. If it's 32767 or 32769 then does not